In recent years, perceived as a problem has been a phenomenon where an active circuit of a portable-type wireless terminal device such as a cellular phone is saturated under an influence of an interference wave, thereby resulting in the deterioration of reception sensitivity of a reception signal.
Hereinafter, an exemplary case where the aforementioned phenomenon causes a problem will be described in detail. In a conventional cellular phone, a connection between an antenna and a reception circuit and a connection between the antenna and a transmission circuit are switched between each other, thereby alternately performing reception and transmission. However, a next-generation cellular phone, which will utilize a transmission/reception scheme typified by a W-CDMA (Wideband Code Division Multiple Access) scheme or the like, generally uses an antenna duplexer to perform simultaneous transmission and reception, without performing a circuit connection switching as described above. In the case of using such a transmission/reception scheme typified by the W-CDMA scheme or the like which does not perform such a circuit connection switching, a transmission signal may leak from the transmission circuit into the reception circuit. The transmission signal leaked into the reception circuit becomes an interference wave. Under the influence of such an interference wave, the reception sensitivity is deteriorated, thereby causing the aforementioned phenomenon.
In general, a conventional wireless circuit device suppresses the deterioration of the reception sensitivity caused by the influence of the interference wave by (1) increasing a size of a passive component such as a filter or by (2) causing an active component, such as an amplifier or mixer, capable of increasing current consumption to have a high linearity (i.e., increasing a size of a battery).
In order to address a problem of increased size as described above, there is a radio disclosed in patent document 1 as an example of a wireless circuit device realizing a small-sized portable terminal. FIG. 17 is a block diagram illustrating a functional configuration of the radio disclosed in patent document 1. The radio shown in FIG. 17 detects, in an RSSI1, an output level of a BPF1 having a characteristic which only passes a signal bandwidth and also detects, in an RSSI2, an output level of a BPF2 having a characteristic which passes a bandwidth of an entire system, thereby controlling a current flowing into the reception circuit based on a comparison between the aforementioned two output levels. As such, the deterioration of the reception sensitivity caused by the influence of the interference wave is suppressed.
Alternatively, there is a wireless transmitter/receiver disclosed in patent document 2 as another example of the wireless circuit device realizing the small-sized portable terminal. FIG. 18 is a block diagram illustrating a functional configuration of the wireless transmitter/receiver disclosed in patent document 2. The wireless transmitter/receiver shown in FIG. 18 operates in a second mode where, when a wireless signal is transmitted, the current consumption is large while a low distortion can be realized. On the other hand, the wireless transmitter/receiver operates in a first mode where, when no wireless signal is transmitted, the current consumption is small. As such, the deterioration of the reception sensitivity caused by the influence of the interference wave is suppressed.
Still alternatively, there is a wireless receiving device disclosed in patent document 3 as another example of the wireless circuit device realizing the small-sized portable terminal. FIG. 19 is a diagram illustrating a block diagram of a functional configuration of the wireless receiving device disclosed in patent document 3. The wireless receiving device shown in FIG. 19 operates in a mode where, when a wireless signal is transmitted, a current flowing into a mixer of the reception circuit is controlled so as to increase not only a current consumption of the mixer but also an injection level of local electrical power. On the other hand, the wireless receiving device operates in another mode where, when no wireless signal is transmitted, the current consumption of the mixer is small and the injection level of local electrical power is also small.    [Patent document 1] Japanese Laid-Open Patent Publication No. 10-256930    [Patent document 2] Japanese Laid-Open Patent Publication No. 11-274968    [Patent document 3] Japanese Laid-Open Patent Publication No. 2003-283361